In accordance with a first alternative of such power semiconductor modules, the substrates can be mounted on a common metallic backplane forming the base plate of the module and via which the heat given off by the power semiconductor chip is dissipated by a heat sink.
In a second alternative of power semiconductor modules, there is no common metallic backplane for the substrates, the bottom side facing the outside of the module forming the bottom side of the module. In modules of this kind, the substrates are mounted in thermal contact with a heat sink without an interposed common backplane.
To optimize dissipation of the heat materializing in the power semiconductor chips mounted on the substrates, the thermal transition resistance between the substrate and the heat sink needs to be as even as possible, this in turn necessitating a force urging the substrate into contact with the heat sink mounting the power semiconductor module.
In conventional power semiconductor modules, this contact pressure force is significantly determined by the force with which the power semiconductor module as a whole is urged against the heat sink, for example by screw fastening.
However, this latter force is generally much higher than the force needed to bring the substrates into contact with the heat sink. It is particularly when the substrates are engineered as metalized ceramic platelets that there is then a risk of the ceramic platelet becoming fractured by an excessive contact pressure.
Hence, there is a need to provide a power semiconductor module fixably bonded to a heat sink and comprising a substrate experiencing, by being mounted on the heat sink, a force urging it in the direction of the heat sink but which is substantially independent of the contact pressure force with which the power semiconductor module is urged against the heat sink.
A further need is to define a method for fabricating such a power semiconductor module.